Why building more roads has environmental effects and won't ease gridlock in the long run

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This week:

There's controversy over a plan to build a new four-to-six lane highway in the Greater Toronto Area. 

The government says the proposed Highway 413 (or GTA West Corridor) will ease congestion, while environmental groups estimate that by 2050, it will boost vehicle emissions by 700,000 tonnes a year and will have generated a total of $1.4 billion in health impacts and ecological damage from air pollution. It will also have paved over carbon-sequestering protected areas.

To be sure, congestion has lots of negative impacts — including environmental ones. Time spent in traffic translates into lost productivity, more collisions and vehicle-related deaths, more greenhouse gas emissions and more air pollutants that cause negative health impacts, such as respiratory problems and cancer, said Fanny Tremblay-Racicot, an assistant professor who researches sustainable development at École nationale d'administration publique (the University of Public Administration) in Quebec.

Tremblay-Racicot also noted that people who live closer to highways are at greater risk of environmental fallout and tend to be disadvantaged populations. "So from an inequity standpoint, you have issues also."

Michael Manville, an associate professor of urban planning at the University of California Los Angeles, said an even bigger negative social impact of congestion is it makes residents and politicians reluctant to build more housing in big cities such as L.A. or Toronto for fear of worsening traffic problems, making housing scarce and unaffordable.

But does building more highways actually ease congestion and reduce these negative impacts? 

Yes, briefly, Tremblay-Racicot said, "but it increases [congestion] in the medium or long run."

That can happen in as few as three to five years, she said, because of a well-documented phenomenon known as induced demand, where traffic quickly increases to fill up the extra capacity because of behavioural changes such as people driving more or changing routes.

Manville acknowledges that's not intuitive — if the road is full, it seems obvious we need more road. But he said that apparent solution ignores "that key insight from economics 101 that says supply and demand are mediated by price."

He said the reason we have a shortage of road space but not a shortage of other things we need to drive — such as cars or fuel — is because roads are free to use. 

"If the goal is to make it so that the driving experience is better and less congested, widening the lane isn't going to help," he said. "The only thing that helps is pricing."

Evidence from places that have road tolls or congestion pricing — such as Singapore and London or even Ontario, home to Highway 407 — shows that it works in reducing traffic levels and delays.